Reproduction of sound



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REPRODUCTION 0F SOUND Filed Feb. 2, 1945 N INVENToR. 4 Q HA @om E #Ay/vis BY HrroR/vy Y d l y Patented Feb. 22, A1949 UNITED STATES PATENT oEFlcE REPRODUCTION OF SOUND Harold E. Haynes, Indianapolis, Ind., assigner to Radio Corporation of America, a. corporation of Delaware Application February 2, 1945, Serial No. 575,885

Claims.

This invention relates to the reproduction of lsound from photographic sound records or the like, and more particularly to the provision of an improved sound reproducing apparatus and method of operation whereby a sound record made without noise reduction may have sound reproduced from it with less background noise than that heretofore involved in the reproduction of sound from such a record.

The present invention is related to that disclosed by a copending application of John R. Cooney, Serial No. 530,415, filed April 10, 1944. The two inventions are similar in that they both involve scanning of the sound track by a light spot which originates at the iiuorescent screen of a cathode ray tube and tends alwaysA to be driven by means including a feedback circuit toward the Opageneaioi,.areliable.nii1,s0llndifk S0 that thenigmmt is maintained astridie boundary line between the tran paren an opal'rea'mord. The two inventions differ in that the present invention (1) dispenses with the light wedge of the aforesaid copending application and relies altogether on the movement of the sound boundary track with respect to the light spot for deriving the audio modulation, and (2) high frequency oscillations are applied to the contro1 grid of the cathode ray tube or to the phototube for providing the audio impulses with a carrier which simplifies the problem of amplifying the output of the phototube.

In the ordinary sound film reproducing system, the instantaneous value of light transmitted through the film is measured and the variation of this light with time constitutes the audio wave contained in the record. In the case of the variable width record, it is the position of the boundary between the opaque and transparent areas which is the inherent measure of the instantaneous voltages recorded, and not the light-transmitting property of the transparent area. The present invention provides an improved means of reproducing sound from a variable width sound track by recognizing the position of this boundary from instant to instant.

The principal object of the present invention is to provide an improved apparatus and method of operation whereby a sound record made without background noise reduction may have sound reproduced from it with less background noise than that heretofore involved in the reproduction of sound from such a record.

The invention will be better understood from the following description considered in connection with the accompanying drawings, and its scope is indicated by the appended claims.

Referring to the drawings:

Figure 1 is a diagrammatic representation of a preferred embodiment of the invention, and

Figure 2 is an explanatory diagram illustrating the path followed by the light spot as it is moved transversely of the SQIIILLLEQILJMQEEQDSQ to the am t' 'n...t..he.ainplitudani.theireaorded @wie "r The sound reproducing apparatus of Fig. 1 includes a cathode ray tube IIJ which has the usual electron gun or beam producing means such as a cathode I I, a grid I2 for controlling the intensity of the beam, a rst anode I3 and whatever other electrodes are required for properly focusing the beam. At its enlarged end, the tube I0 is provided with a uorescent screen upon which aspot of light is produced by impingement of the beam on the screen. The tube I 0 may include a second anode I4 and a pair of deflectors i5 and I6 for moving the beam transyerselypfa soundrecord I'I. A voltage divider or other suitable'iars''not illustrated) is provided for maintaining the various electrodes of the tube I0 at such potentials as are required for proper operation of the tube I0. A high frequencyoscillatgr I8 may be connected to the grid I2 for varying the potential of the grid I2 at a superaudible frequency or may be associated with a phototube I9 which receives light modulated by the record I'I. If the oscillator I8 is connected to the grid I2, it is desirable that the tube I 0 be of the short-persistence type so that the spot intensity itself will be modulated. If it is connected to the phototube I9, the iluorescent screen of the tube I0 may be such as to permit somewhat longer persistence of the light spot.

The light spot which is indicated at :con the iluorescent screen can move only in the path L--R as indicated in Fig. 2. An image of this path is formed on the record I'I by a cylindrical lens 20 which is positioned parallel with the record I1 and at right angles to the motion of this record as indicated by the arrow adjacent to the edge of the record.

With the oscillator connected to the control grid I2 of the tube I0, the spot :r is modulated in intensity at a frequency well above the highest audio frequency recorded on the record l1. IIhe light thus modulated is passed through the record I'I to the phototube I9. The output of the phototube I9, which is a. high frequency alternating voltage (or carrier) amplitude-modulated by the audio signal, is amplified by the amplifier 2|. Since the signal is analogous to an ordinary amplitude-modulated radio signal, the amplifler 2l may be a tuned amplifier similar to the intermediate frequency amplier of a radio receiver. Thus, the modulating signal is detected by the detector 22, and any of the carrier passed by the detector is dissipated in the filter 23.

This fluctuating unidirectional potential is applied (1) through a coupling capacitor 25 to a utilization device such as an audio amplifier and a loud speaker and (2) through a lead 26 to the deector I5 in such a phase relation that it tends always to drive the image of the bright spot 1: toward the opaque area of the record I1.

If the spot :c moves over into the opaque area, however, the signal received by the phototube .drops to zero and no voltage is available to keep the spot so deflected. In other words, if the overall gain is very high so that only a small fraction of the light contained in the spot is suicient to produce voltage high enough to deect the spot the full width of the track, then the spot will follow the contour of the recorded wave faithfully with only a small portion of it spilling over into the clear area to provide deflecting l voltage.

Since the spot deflection on the record l'l is proportional to the voltage applied to the deflecting plate l5, providing beam deection in the cathode ray tube is proportional to the voltage difference between electrodes l5 and I6 and providing that the spot movement at the lm is a replica of the spot movement on the screen (except for size), this voltage necessarily is the audio voltage contained in the sound track of the record and appears at the terminal 24 at a quite high level.

A source of bias potential 28 may be provided in the lead of the deflector I6 for biasing the spot :E to any desired point in the path L-R of Fig. 2.

Another way of utilizing the carrier Wave principle is to omit the intensity modulation of the electron beam of the tube l0 and apply as a polarizing voltage to the phototube a carrier frequency potential. In this case, the fluorescent screen of the tube l0 need not have such short persistence as in the previous case since the spot :i: is required only to follow the highest frequency recorded on the record l1. In either case the beam applied to the record is subjected to a carrier frequency. Appended claims calling for this feature are therefore intended to cover either case unless otherwise limited.

' I claim as my invention:

1. In a device for reproducing sound from a variable Width sound record, means for producing a. light spot which varies in intensity at a superaudible frequency, and means responsive to light transmitted through said record for moving said spot in accordance with the contour of the boundary between the opaque and transparent areas of said record.

2. The combination of means for producing a light spot which varies in intensity at a superaudible frequency, a light sensitive device responsive to light transmitted from said spot through a sound record having adjacent opaque and transparent areas, an amplifier tuned to said superaudible frequency for amplifying the output of said light sensitive device, means for eliminating the superaudible component of said amplified output, and means responsive to the remaining component of said output for moving said spot in accordance with the contour of the boundary between said opaque .and transparent areas.

3. The combination of means for producing a light spot which varies in intensity at a superaudible frequency, a light sensitive device responsive to light transmitted from said spot through a sound record having adjacent opaque and transparent areas, an amplifier tuned to said superaudible frequency for amplifying the output of said light sensitive device, means for eliminating the superaudible component of said amplified output, means responsive to the remaining componentof said output for moving said spot in accordance with the contour of the boundary -between said opaque and transparent areas, and means for supplying a part of said remaining component to a utilization circuit.

4. In a device for reproducing sound from a -record wherein transparent and opaque areas are defined by a boundary having a contour which varies in accordance with said sound, the combination of means for applying a beam of light to said record, means for varying the intensity of said beam at a frequency which is high .with respect to the frequency of said sound, and means responsive to light transmitted through said transparent area for maintaining said beam at said boundary.

5. In a device for reproducing sound from a record wherein transparent and opaque areas are defined by a boundary having a contour which varies in accordance with said sound, the combination of means for applying a beam of light to said record, means for varying the intensity of said beam at a frequency which is high with respect to the frequency of said sound, and

means responsive to light transmitted through said transparent area for maintaining said beam at said boundary, and means responsive to said transmitted light for deriving an audio frequency current dependent on the position of said beam.

HAROLD E. HAYNES.

REFERENCES CITED The following references are of record in the le of this patent UN'ITED STATES PATENTS Number Name Date 1,974,900 Shoup Sept. 25, 1934 2,017,901 Huffman Oct. 22, 1935 2,121,211 Padva et a1 June 21, 1938 2,277,502 Padva Mar. 24, 1942 2,347,084 Cooney Apr. 18, 1944 FOREIGN PATENTS Number Country vDate 8108/32 Australia July 5, 1933 434,936 Great Britain Sent. 11. 1935 

